Gear shaping apparatus with improved cutter retraction arrangement

ABSTRACT

A gear shaping apparatus in which a spindle with the cutting wheel thereon is movable axially from its normal operating range to a retracted position to facillitate insertion and removal of the work piece. A retracting drive is provided separate from the stroke drive which reciprocates the spindle axially for normal cutting. For retraction of the spindle, the stroke drive is first disengaged from its driving connection to the spindle, after which the retracting drive is drivingly engaged with the spindle to retract the same. The retracting drive may be a fluid operated piston and cylinder unit operably connected to the spindle or a separate motor attached to a shaft which is permanently drivingly engaged with the spindle.

Jan. 8, 1974 Miller GEAR SHAPING APPARATUS WITH IMPROVED CUTTERRETRACTION ARRANGEMENT Primary Examiner-Francis S. l-lusar [75]Inventor: Walter Seiberlich, Ettlingen, 141w y Larson et Germany T C m SB A n 5 n e 00 Zn mm t mE fl e ma we fi k MA a e n b S S Germany A gearshaping apparatus in which a spindle with the [22] Filed: Sept 25, 1972cutting wheel thereon is movable axially from its normal operating rangeto a retracted position to facillitate insertion and removal of the workpiece. A re- [21] Appl. No.: 291,566

tracting drive is provided separate from the stroke [30] ForeignApplication Priority Data drive which reciprocates the spindle axiallyfor normal cutting. For retraction of the spindle, the stroke drive isfirst disengaged from its driving connection to the Sept. 25, 1971Germany................... P 21 47 923.2

spindle, after which the retracting drive is drivingly engaged with thespindle to retract the same. The retracting drive may be a fluidoperated piston and cyl inder unit operably connected to the spindle ora sepa- 00 0m .3 W3 2 MB ".0 c Ur Ha e S C d std U..mF an 555 rate motorattached to a shaft which is permanently References Cited drivinglyengaged with the spindle. UNITED STATES PATENTS 3,225,658Levanovich............................... 90/7 15 Claims, '5 DrawingFigures GEAR SHAPING APPARATUS WITH IMPROVED CUTTER RETRACTIONARRANGEMENT BACKGROUND OF THE INVENTION which itself has the appearanceof a gear. When operating according to this process, the distancebetween the axes of the cutting wheel and the work piece are determinedwhen cutting outside teeth by the sum of the radii of the pitch circles,and when cutting inside teeth by the difference of the radii of thepitch circles. Either the work piece or the cutting wheel can be movedradially towards each other during the cutting operation.

' The work piece and the cutter wheel are connected with one another byway of gear trains at a transmission ratio related to the inverse valueof the number of teeth or the radii of the pitch circles of the workpiece and the cutter wheel. In known gear shapers, the rotationalmovement between the cutter wheel and the work piece is provided bymeans of gear trains having fixed transmission ratios.

For producing the gear profile on the work piece, it

is necessary to move the cutter wheel axially through a double stroke,i.e., through the work piece and back, in addition to the rotationalmovement. As the cutting wheel moves axially through the work piececoncurrent with the rotational movement of the cutting wheel and thework piece, the raw material is cut out of the work piece. For thereturn stroke following each operating stroke, the cutter wheel and thework piece are separated by moving the cutter wheel away from the workpiece or vice versa so that the cutter wheel can return to its startingposition without contacting the work piece. This lifting movement of thecutter wheel relative to the work piece takes place, depending on thetype and shape of the tooth that is being produced, either in thedirection of the line connecting the centers of the cutter wheel and thework piece or at an angle to this line and this movement is imparted bya corresponding control of the cutter wheel spindle or of the workpiece. A means for controlling this movement is shown for example in theDitchler US. Pat. No. 3,587,384 issued June 28, 1971.

The length of the operating and return strokes can be adjusted,depending on the width of the teeth being cut through the work piece.When inside teeth are being cut, which teeth are located far beneath theupper edge of the hollow body in which the teeth are located, themounting and dismounting of the work piece can cause difficulties,particularly in the case of large work pieces. To avoid this problem, itis necessary to retract the cutter wheel completely out of this hollowbody.

A gear shaping apparatus of the above described type is shown anddescribed in US. Pat. No. 3,225,658. In this case, the pivoting point ofa driving arm which movesthe cutter wheel spindle up and down is mountedin a yoke, which, whenever the spindle stroking mechanism is stopped inits lower dead center position, is moved hydraulically upwards and, as aresult thereof, also moves the spindle of the cutter wheel upward to aretracted position, whereby the cutter wheel can be moved above theupper edge of a large hollow work piece for mounting and dismounting thesame. However, such known constructions have the disadvantage that theretracting movement can be made only with difficulty and that themachine is not well suited for high loads because of the movable yokelying in the gear train of the operating stroke drive and also becauseof the relatively large number of movable parts required in the overalldrive arrangement for providing both normal operating stroke axialmovement and retraction movement. This disadvantage becomes particularlynoticable when the machine does not cut by pushing from the top but bypulling through the work piece from the bottom.

Furthermore, arrangements have been known by which the chucking fixtureused for connecting the work piece to the work table is capable ofmoving downwardly, for example by a hydraulic mechanism. However, thisarrangement can be used only in the case of relatively small workpieces. In the case of large work pieces, the chucking arrangementbecomes so large that it can no longer be retracted to clear the cutterwheel spindle from the work piece for laterally removing the work piecefrom the work table.

Thus, there exists a need in gear shaping apparatus of the typedescribed for an improved arrangement for retracting the cutter wheelrelative to the work piece.

SUMMARY OF THE INVENTION Thus, it is a purpose of this invention toprovide a gear shaping apparatus of the type described in which thepreviously mentioned disadvantages of known apparatus will be avoided.

This purpose of the present invention is achieved by providing anarrangement wherein after the cutting procedure is completed, the drivemeans which drives the spindle through its normal operating range duringthe cutting procedure can be disengaged from the spindle, at which timean additional drive means becomes operable to move the spindle to theretracted position. In the case of the customary design of the gearshaping apparatus which includes as a stroke drive a stroking gearconnected via a cam means and a connecting rod to a rocking arm which isin turn connected to a lifting wheel which actually engages the spindle,the present invention may take the form of an arrangement whichdrivingly disengages the rocker arm or rocker arms from the liftingwheel whereupon the said additional drive becomes effective to lift thespindle and the cutting wheel to the retracted position, clearing thework piece.

With the spindle thus disengaged from the normal operating stroke drive,any suitable means may be utilized for retracting the spindle with itscutting wheel thereon. For example, in one arrangement, the additionaldrive may comprise a lifting piston and cylinder unit, the piston ofwhich is firmly connected to the spindle of the cutter wheel, whichcylinder preferably and at the same time also constitutes part of aknown hydraulic weight compensating and shock absorbing system on thespindle as shown for example in the German Democratic Republic Pat. No.52,043. Only a slight modification of this structure would be requiredto adapt the same for use as the additional drive of the presentinvention. In another embodiment, this additional drive for retractingthe spindle could take the form of a separate motor releasably drivinglyengaged with the shaft of the lifting wheel which remains engaged withthe spindle even after it has been separated from the rocker arm orarms.

Suitable control means may be provided for automatically disengaging thestroke drive from the spindle and operating the additional drive uponcompletion of the gear cutting operation.

Thus, it is an object of this invention to provide a new and improvedarrangement in a gear shaping apparatus for separating the cutter wheelfrom the work piece for mounting and dismounting of the latter.

It is another object of this invention to provide in a gear shapingapparatus of the type having a cutter wheel mounted on a spindle whichmoves axially during a normal cutting stroke, a means for retracting thespindle for mounting and dismounting of the work piece by disengagingthe usual spindle stroke drive and utilizing a separate additional drivefor retracting the spindle.

It is another object of this invention to provide, in a gear shapingapparatus of the type described which includes the customary strokedrive of a stroking gear, a cam, a connecting rod and rocker armsdrivingly engaged with the spindle via a lifting wheel, a means fordisengaging this normal stroke drive by separating the lifting wheelfrom the rocker arms whereby the additional drive may then be operatedto lift the spindle without also requiring the following movements ofthe conventional stroke drive.

Other objects and other advantages of the invention will become moreapparent from the detailed description to follow, together with theaccompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS There follows a detailed descriptionof preferred embodiments of the invention which are to be read togetherwith the accompanying drawings.

FIG. 1 is a schematic view showing the relevant parts of a gear shapingapparatus including the features of the present invention.

FIG. 2 is a schematic view showing on the right hand side thereof aportion which is a cross-section taken along line 2-2 of FIG. 1, on thelefthand side thereof, an enlargement of the upper part of FIG. 1,together with lines illustrating schematically the hydraulic circuit foroperating the present invention.

FIG. 3 illustrates another embodiment of the invention. The lower partof this figure is a cross-section taken along line 2-2 of FIG. 1, andthe added features of this other embodiment are shown towards the upperportion thereof, and the hydraulic circuit for operating the embodimentof FIG. 3 is also shown therein.

FIG. 4 is a circuit diagram of the control means for automaticallyoperating the embodiment of FIGS. 1 and 2.

FIG. 5. is a circuit diagram illustrating the circuit for automaticallyoperating the embodiment of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to thedrawings, like elements are represented by like numerals throughout theseveral views.

Referring now to FIGS. 1 and 2, the drive motor 1 of the gear shapingapparatus drives a continuous cone pulley looping gear mechanism 3 via abelt drive 2 and a stroke gear 7 via intermediate gears 4, 5, and 6. Aconnecting rod 9 is coupled with the stroke gear 7 by means of a pin 8,which connecting rod 9 changes the rotational movement indicated byarrow 10 to an oscillating circular movement indicated by arrow 11. Atwoarmed rocker arm 12 is connected with a lifting wheel 14 by a set ofteeth 13 located on each side of the lifting wheel 14, each set engagingmating teeth on one of the two rocker arms 12.

The rocker arms 12 are urged into driving engagement with the liftingwheel 14 by means of springs 16 mounted on a pin 15. Two such pin andspring arrangements are shown in FIG. 2, the righthand one of whichurges the lowermost rocker arm of FIG. 2 into engagement with liftingwheel 14 and the lefthand arrangement urges the uppermost rocker arm 12of FIG. 2 into engagement with the lifting wheel 14. As shown in thedrawings, the springs comprise a package, i.e., a series of Bellvillesprings. Between the lifting wheel 14 and each rocker arm there isprovided an annular piston 17. Pressure fluid from line 60 passesthrough axial passage 61 and radial passage 18 to chambers 59 locatedinteriorly of annular piston 17, i.e., between the inner surfacesthereof and the lifting wheel 14. To separate the rocker arms 12 fromthe lifting wheel 14, fluid is introduced through the above describedlines to chamber 59 whereupon the fluid urges the pistons 17 outwardlyseparating the teeth 13. When the rocker arms 12 are thus separated, thelifting wheel 14 is free to rotate relative to the rocker arms 12.During such relative rotation, the pistons 17 rotate with the liftingwheel 14. The outer heads on pins 15 are free to rotate within therespective rocker arms 12 into which they extend because the recess 62into which the pins 15 are inserted extend circumferentially, or atleast a T-shaped crosssection portion 63 extends circumferentiallyaround the axis of rocker arm 12.

The spindle 20 on which the cutter wheel is attached has a sleeve 19attached thereon with annular teeth extending thereabout. The teeth 14alocated about the circumference of lifting wheel 14 engage these annularteeth on sleeve 19 such that oscillating motion 11 of the rocker arm 12and the lifting wheel 14 will cause recip rocating vertical movement ofthe spindle 20.

The cutter wheel 21 is shown attached to the lower end of spindle 20.FIG. 1 also shows three positions including an upper retracted position21a, and lower normal operating end positions 21b (shown in solid lines)and 21c. The normal operating range which is the distance betweenpositions 21b and 21c is represented by the distance H in FIG. 1.

The turning movement of the cutter wheel and of the work piece isaccomplished by means of motor 22. The rotational movement of this motoris transferred via shaft 23 and interengaging bevel gears 24 and 25 to ashaft 26 the latter of which in turn operates a worm gear 27 which turnsa worm wheel 28. Worm wheel 28 is fixed to the casing portion 29 whichturns with it. An axial passage in 29 receives a spline 30 on the member30a which is fixed to the spindle 20. Thus, turning the worm wheel 28acts through elements 29, 30 and 30a to turn the spindle 20 while thelatter is still free to move axially via spline 30a.

The rotational movement of shaft 23 also provides rotational movement ofthe work piece 42. For this purpose, shaft 23 is connected to a spurgear 31 engaged with spur gear 32 which transmits the rotary'motion viabevel gears 33 and 34, shaft 35, speed changing gears 36 and 37, shaft38 and worm gear 39 to the worm wheel 40 which turns the work table 41on which the work piece 42 is mounted. A suitable chucking fixture suchas 43 is provided for holding the work piece 42 onto the work table 41.Also shown in FIG. 1 is a dotted line position 41a of the work table andthe work piece. At this position 41a of the work piece is fixed onto thework table, after which the latter is moved to the solid line positionshown in the. drawings, and to which position the workpiece and the worktable are moved for removal of the work piece after cutting has beencompleted. I

A hydraulic system providing weight compensation,-

shock absorption and also the means for raising and lowering the spindleis best shown in FIG. 2. A small piston 44 located within a fixedcylinder 64 has a lower surface 46. Surrounding this fixed cylinder 64is an annular piston 45 urged downwardly by spring package, i.e.,Bellville springs 45a, and adapted to be urged upwardly by pressurefluid introduced through passage 68 and applied against the lowersurface 47 of piston 45. Piston 45 also includes a passageway 67extending therethrough and connecting fixed openings 65 and 66 forintroducing fluid into the cylinder 64 beneath piston 44. A vent opening69 is provided above the piston 45.

While the operation of the invention will be described in greater detailbelow, it will be convenient to describe at this point, movement of theelements 44 and 45 when the cutter wheel 21 moves between normaloperating positions 21b and 210. At this time the spaces beneath pistons44 and 45 are in communication with each other through openings 66 and66a, and these areas are otherwise closed off. When the piston 44 movesdownwardly, fluid moves through openings 66 and 66a and against thesurface 47 beneath piston 45. Piston 45 then rises, compressing springs45a; and as spindle 20 rises, fluid passes back through the openings 66and 66a beneath the piston 44. Since area 47 is much greater than area46, movement of piston 44 results in a much smaller movement of piston45. Thus, the springs 45a can be much shorter than would otherwise bethe case.

The lifting gear'l4 is connected firmly rotatably with a shaft 48 onwhich, in addition, the two-armed rocker 12 is freely rotatably mounted.A gear 49 is attached to one end of the shaft and this engages anadditional gear 50 at a ratio of 2:1, which latter gear is coupled witha cam drum 51. Trip cams 51a can be attached adjust ably in grooves onthe drum, and these cams operate terminal switches 52 which in turncontrol the flow of current to magnetically operated solenoid valves 53and 54, the former controlling the flow of hydraulic fluid fromreservoir R to chambers 59, and the latter controlling the flow of fluidfrom reservoir R to the space beneath piston 44. Also shown in thedrawing is a solenoid valve 55 and a pump 56 for controlling the flow offluid .to and from the space beneath piston 45.

The control circuit for operating the embodiment of FIGS. 1 and 2 isshown schematically in FIG. 4. In series with the switch 52 are furtherswitches 90 and 91 which respond to the cutter wheel reaching thepredetermined depth in the work piece and the completion of a certainnumber of complete trips of the cutter wheel around the work piece,respectively. When all three of these switches have been closed, currentcan be delivered to operate the solenoids associated with valves 53, 54and 55, the purposes for which will become more apparent in thefollowing description of the operation of the invention.

The embodiment of FIGS. 1 and 2 operates as follows:

In the starting position the work table is at position 41a whereat thework piece is mounted thereon. The stroking gear 7 is at its lower deadcenter position and the cutter wheel is at its retracted position 12a.The work piece on the work table is then moved to the solid lineposition shown in the drawings. At this time, piston is in the positionshown in the drawings whereby pressurized fluid has been deliveredthrough these openings to the space beneath piston 44 which is raised tothe top of its cylinder so that cutter wheel 21 is in position 21a. Atthis time, fluid has also been delivered from reservoir R through valve53 to the spaces 59 to urge the pistons 17 outwardly. At this time alsovalve is in position to release fluid from the space beneath piston 45to the reservoir R thus permitting piston 45 to move downwardly to theposition shown in the drawings.

With the work piece now in place, piston 44 and hence spindle 20 arelowered to the position shown in the drawings by moving the valve 54 sothat the fluid beneath piston 44 can pass through openings -67 andthrough the valve 54 to reservoir. Fluid is then introduced via pump 56and valve 55 to passage 68 and this raises piston 45, placing opening 67out of communication with openings 65 and 66. This hydraulic system isnow capable of functioning as a closed weight compensating and shockabsorbing system in the manner described earlier. The valve 53 is nowoperated to drain fluid from passage 59 so that springs 16 are operableto engage elements 12 and 14 via gear teeth 13.

The cutter wheel is now operated in the manner known per se to effectcutting. That is, the cutter wheel 21 and work piece 42 are rotated bymotor 22 in the manner described above and the spindle 20 isreciprocated via elements 1-14 and 19 in the manner described above. Thespecific procedure for adjusting all relative machine values to providethe correct profile in work piece 42 is known per se and will not bedescribed herein. However, some details thereof are described in theabove mentioned Ditchler patent, the bove described U.S. Pat. No.3,225,658, and in the copending commonly owned U.S. application Ser. No.176,055, filed Aug. 30, 1971 and now U.S. Pat. No. 3,722,359.

During each operating stroke between positions 21b and 21c, the cutterwheel 21 cuts during movement in one direction and is moved clear of thework piece for movement in the opposite direction. For such clearingmovement, either the work piece or the cutter wheel can be moved. In thepresent embodiment, the cutter wheel would be moved away from the workpiece. This is accomplished by rotating the spindle 21 about a pivotaxis perpendicular tothe plane of FIG. 1 and passing through the centerof worm gear 27. This movement is very slight, perhaps 0.5 millimeters.Hence, the teeth on sleeve 19 will not move off of the teeth on liftingwheel 14. Also, the turning movement of worm gear 27 is so slight thatthe tolerance in its spline connection to shaft 26 will permit thenecessary movement of this gear 27 while the latter remains properlyengaged with gear 28.

When the cutting of work piece 42 has been completed, the lifting wheel14 is at the end position 21b at which time cam 51a closes switch 52. Atthis time, switches 90 and 91 are also closed. Valve 53 is then operatedto deliver fluid from the reservoir to the chambers 59 via passages 60,61 and 18 to disengage the lifting wheel 14 from rocker arms 12. Valve55 is operated to connect the area beneath 45 directly with thereservoir to drain the fluid through passage 68, as a result of which 45moves to the position shown in the drawings connecting passage 67 topassages 65 and 66. Meanwhile, valve 54 is moved to the position fordelivering fluid from the reservoir through the pump P to the spacebeneath piston 44 to raise the latter and hence also raise and retractthe spindle and the cutter wheel 21. The work table 41 will now be movedlaterally to the position 41a whereat the work piece 42 can easily beunclamped, removed, and a new work piece mounted thereon. The cycle thenrepeats itself.

FIG. 3 illustrates another embodiment of the invention. This embodimentis similar to the embodiment of FIGS. 1 and 2 except that the retractingdrive, instead of being the hydraulic piston and cylinder unit shown inFIG. 2 is a separate drive which is drivingly engaged with the shaft 48.

Referring to FIG. 3, there is shown a motor 77 which drives a shaftconnected to worm gear 78 which in turn drives worm wheel 79 and henceshaft 80 fixed thereto. This shaft enters a friction clutch 81, on theoutput side of which is a shaft 82 connected to gears 76 and 75, thelatter fixed with shaft 48.

A valve 83 operates to introduce pressurized fluid to a passage 84 and achamber 85 behind piston 86. Piston 86 is slidable along a member 88which is rigid with shaft but it is rotatable with this member 88. Itincludes disc plates thereon. Interleaved disc plates are attached to afurther member 89 which is fixed to the output shaft 82. Fluid inchamber urges piston 86 axially to move the discs of elements 86 and 89into engagement with each other, whereby the rotating motion of shaft 80is transmitted to the shaft 82. In other respects, the embodiment ofFIG. 3 is identical to that of FIGS. 1 and 2 except of course for theface that the hydraulic piston and cylinder unit above spindle 20 wouldno longer need to serve the purpose of raising and lowering the spindle,and hence these elements could assume their function as known heretoforeas acting as a weight compensating and shock absorbing means.

The embodiment of FIG. 3 operates in essentially the same manner as theembodiment of FIGS. 1 and 2, and hence the operation will not beexplained in detail except for the differences. In this embodiment, andreferring also to FIG. 5, when switches 52, 90 and 91 have been closed,current is delivered to operate the valve 53 and the motor 77. It willbe recalled that switch 52 depended on the angular position of shaft 48.However, in the embodiment of FIG. 3, the retracting drive will turn 48and hence tend to open switch 52. To prevent this, a suitable holdingrelay 92 can be provided. Fluid is now delivered from pump P throughvalve 53 to chamber 59 to disengage rocker arms 12 from lifting wheel14. At this time, the fluid passing valve 53 passes into line 53 a andopens pressure responsive valve 83 to transmit fluid into the clutch 81in the manner described above whereby shafts 80 and 82 are drivinglyengaged, the latter turning elements 75, 76 and 48 to turn the liftingwheel to retract the spindle 20. In a preferred mode of operation, themotor 77 operates continuously. It is also possible for this motor to benormally off and to have it operated by a line parallel to the line inFIG. 5 including the solenoid of valve 53 as shown in dotted lines inFIG. 5. To start a new cycle, the spindle is lowered after which valve53 is moved back to the position shown in FIG. 3 whereby fluid isdrained from the clutch 81 and from the chambers 59, whereby theelements 12 and 14 again engage, and clutch 81 disengages.

FIG. 1 also illustrates the means referred to above for removing thecutting wheel 21 from the work piece for the return stroke betweenpositions 21b and 210. For this purpose, a bevel gear 95 engaged withgear 5 turns a shaft 96 which in turn rotates worm gear 97 and wormwheel 98 to rotate cam 99 which in turn rotates rollers 100 and 101which then move the slight distance required to urge the spindle 20slightly to the left (as viewed in FIG. 1).

Although the invention has been described in considerable detail withrespect to preferred embodiments thereof, it will be apparent that theinvention is capable of numerous modifications and variations withoutdeparting from the spirit and scope of the invention.

I claim:

1. A gear shaping apparatus comprising:

a cutter wheel mounted on a spindle,

means mounting the spindle for axial movement through a normal operatingrange between first and second axially spaced positions for cutting awork piece which is the gear to be shaped, and a retracted positionspaced axially from the normal operating range for spacing the cutterwheel from the work piece,

a stroke drive means for driving the spindle between said first andsecond positions for normal cutting operation,

a retracting drive separate from the stroke drive for moving the spindleto the retracted position, said stroke drive being disengagable from itsdriving connection with the spindle,

and means for operating the retracting drive to retract the spindlewhile the stroke drive is disengaged.

2. A gear shaping apparatus according to claim 1,

said stroke drive including:

a lifting wheel, the periphery of which drivingly engages the spindlefor axially moving the same, a rocker arm releasably drivingly engagingthe lifting wheel, and means drivingly engaged with said rocker arm foroscillating the rocker arm to in turn oscillate the lifting wheel toreciprocate the spindle axially,

and means for disengaging the rocker arm from the lifting wheel.

3. A gear shaping apparatus according to claim 2, said rocker arm andsaid lifting wheel being mounted coaxially and including engaging teethon their facing sides, said rocker arm and said lifting wheel beingrelatively axially movable to bring said teeth into and out of drivingengagement.

4. A gear shaping apparatus according to claim 3, including a springmeans urging the rocker arm and the lifting wheel into engagement witheach other, and a servo-piston for separating the rocker arm and thelifting wheel teeth from engagement with each other to permit relativerotation therebetween.

5. A gear shaping apparatus according to claim 4, including a pair ofrocker arms, one of each side of the lifting wheel, both the rocker armshaving teeth engaging opposite sides of the lifting wheel, and includinga servo-piston for each of said rocker arms.

6. A gear shaping apparatus according to claim 2, said retracting drivecomprising a fluid operated piston and cylinder unit operably connectedto said spindle for movement therewith, and means for operating thepiston and cylinder unit to move the spindle to the retracted positionwhen said rocker arm is disengaged.

7. A gear shaping apparatus according to claim 6, said spindle axisbeing vertical, and said piston and cylinder unit including a hydraulicweight compensating and shock absorbing system for compensating for theweight of the spindle and damping shocks during movement of the spindlethrough said normal range.

8. A gear shaping apparatus according to claim 7, including a controlmeans for controlling operation of the piston and cylinderunit, saidcontrol means including three electrical switches in series, whichswitches, when closed, permit the control means to cause the piston andcylinder unit to be operated to move the spindle to the retractedposition, the first of said switches closing whenever the cutter wheelreaches one of said first or second positions, which one is closest tothe retracted position, the second of said switches closing after thecutter wheel has reached a predetermined depth relative to the'workpiece, and the third of said switches closing after completion of acertain number of complete trips of the cutter wheel around the workpiece.

9. A gear shaping apparatus according to claim 8, said first switchbeing operated by a cam which is driven by the said lifting wheel.

10. A gear shaping apparatus according to claim 8, including springmeans for urging the rocker arm and the lifting wheel into engagementwith said other and a servo-piston for separating the rocker arm and thelifting wheel from each other, a solenoid fluid valve forcontrolling theflow of hydraulic fluid to move the spindle to the retracted position, asolenoid fluid valve for controlling the flow of oil to the saidservo-piston, and

said series switches, when closed, providing an electrical current pathto open both of said solenoid valves.

11].. A gear shaping apparatus according to claim 2, said retractingdrive comprising a means for turning the lifting wheel when it isdisengaged from the rocker arm.

12. A gear shaping apparatus according to claim 11, said lifting wheelfixed onto a shaft, a clutch means, one side of such clutch meansdrivingly engaged to said shaft, and the other side of said clutchdrivingly engaged to said retracting drive.

13. A gear shaping apparatus according to claim 12, including a controlmeans for controlling the operation of the said clutch and hencecontrolling the driving the retracted position, the second of saidswitches clos ing after the cutter wheel has reached a predetermineddepth relative to the work piece, and the third of said switches closingafter completion of a certain number of complete trips of the cutterwheel around the work piece.

14. A gear shaping apparatus according to claim 13,

said first switch being operated by a cam which is driven by the saidlifting wheel.

15. A gear shaping apparatus according to claim 13, including a springmeans for urging the rocker arm and the lifting wheel into engagementand including a servo-piston for separating the rocker arm and thelifting wheel from each other, a solenoid fluid valve for controllingthe flow of hydraulic fluid to the said servopiston, and afluid valvefor closing the said clutch, and said series switches, when closed,providing an electrical current to said solenoid valve to open the same,whereby hydraulic fluid flows to said servo-piston to disengage therocker arm and the lifting wheel from each other and to said clutch toengage the same.

1. A gear shaping apparatus comprising: a cutter wheel mounted on aspindle, means mounting the spindle for axial movement through a normaloperating range between first and second axially spaced positions forcutting a work piece which is the gear to be shaped, and a retractedposition spaced axially from the normal operating range for spacing thecutter wheel from the work piece, a stroke drive means for driving thespindle between said first and second positions for normal cuttingoperation, a retracting drive separate from the stroke drive for movingthe spindle to the retracted position, said stroke drive beingdisengagable from its driving connection with the spindle, and means foroperating the retracting drive to retract the spindle while the strokedrive is disengaged.
 2. A gear shaping apparatus according to claim 1,said stroke drive including: a lifting wheel, the periphery of whichdrivingly engages the spindle for axially moving the same, a rocker armreleasably drivingly engaging the lifting wheel, and means drivinglyengaged with said rocker arm for oscillating the rocker arm to in turnoscillate the lifting wheel to reciprocate the spindle axially, andmeans for disengaging the rocker arm from the lifting wheel.
 3. A gearshaping apparatus according to claiM 2, said rocker arm and said liftingwheel being mounted coaxially and including engaging teeth on theirfacing sides, said rocker arm and said lifting wheel being relativelyaxially movable to bring said teeth into and out of driving engagement.4. A gear shaping apparatus according to claim 3, including a springmeans urging the rocker arm and the lifting wheel into engagement witheach other, and a servo-piston for separating the rocker arm and thelifting wheel teeth from engagement with each other to permit relativerotation therebetween.
 5. A gear shaping apparatus according to claim 4,including a pair of rocker arms, one of each side of the lifting wheel,both the rocker arms having teeth engaging opposite sides of the liftingwheel, and including a servo-piston for each of said rocker arms.
 6. Agear shaping apparatus according to claim 2, said retracting drivecomprising a fluid operated piston and cylinder unit operably connectedto said spindle for movement therewith, and means for operating thepiston and cylinder unit to move the spindle to the retracted positionwhen said rocker arm is disengaged.
 7. A gear shaping apparatusaccording to claim 6, said spindle axis being vertical, and said pistonand cylinder unit including a hydraulic weight compensating and shockabsorbing system for compensating for the weight of the spindle anddamping shocks during movement of the spindle through said normal range.8. A gear shaping apparatus according to claim 7, including a controlmeans for controlling operation of the piston and cylinder unit, saidcontrol means including three electrical switches in series, whichswitches, when closed, permit the control means to cause the piston andcylinder unit to be operated to move the spindle to the retractedposition, the first of said switches closing whenever the cutter wheelreaches one of said first or second positions, which one is closest tothe retracted position, the second of said switches closing after thecutter wheel has reached a predetermined depth relative to the workpiece, and the third of said switches closing after completion of acertain number of complete trips of the cutter wheel around the workpiece.
 9. A gear shaping apparatus according to claim 8, said firstswitch being operated by a cam which is driven by the said liftingwheel.
 10. A gear shaping apparatus according to claim 8, includingspring means for urging the rocker arm and the lifting wheel intoengagement with said other and a servo-piston for separating the rockerarm and the lifting wheel from each other, a solenoid fluid valve forcontrolling the flow of hydraulic fluid to move the spindle to theretracted position, a solenoid fluid valve for controlling the flow ofoil to the said servo-piston, and said series switches, when closed,providing an electrical current path to open both of said solenoidvalves.
 11. A gear shaping apparatus according to claim 2, saidretracting drive comprising a means for turning the lifting wheel whenit is disengaged from the rocker arm.
 12. A gear shaping apparatusaccording to claim 11, said lifting wheel fixed onto a shaft, a clutchmeans, one side of such clutch means drivingly engaged to said shaft,and the other side of said clutch drivingly engaged to said retractingdrive.
 13. A gear shaping apparatus according to claim 12, including acontrol means for controlling the operation of the said clutch and hencecontrolling the driving connection between the retracting drive and saidshaft, said control means including three electrical switches in serieswith each other, which switches, when closed, cause the shaft to beturned by means of said retracting drive to retract the lifting wheel,the first of said switches closing whenever the cutter wheel reaches oneof said first or second positions, which one is closest to the retractedposition, the second of said switches closing after the cutter wheel hasreached a predetermined depth relative to the work piece, and the thirdof sAid switches closing after completion of a certain number ofcomplete trips of the cutter wheel around the work piece.
 14. A gearshaping apparatus according to claim 13, said first switch beingoperated by a cam which is driven by the said lifting wheel.
 15. A gearshaping apparatus according to claim 13, including a spring means forurging the rocker arm and the lifting wheel into engagement andincluding a servo-piston for separating the rocker arm and the liftingwheel from each other, a solenoid fluid valve for controlling the flowof hydraulic fluid to the said servo-piston, and a fluid valve forclosing the said clutch, and said series switches, when closed,providing an electrical current to said solenoid valve to open the same,whereby hydraulic fluid flows to said servo-piston to disengage therocker arm and the lifting wheel from each other and to said clutch toengage the same.